Magnet-core.



G. W. ELMEN.

MAGNET CORE.

APPLICATION FILED APR. 6. I916. RENEWED JUNE 27. 1918.

1,26,965. Patented Dec. 10, 1918.

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GUSTAF W. ELMEN, 0F BOGOTA, NEW JERSEY, ASSIGIQTOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, 013 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MAGNET-CORE.

Specification of Letters Patent.

Patented Dec. 10, 1918.

Application filed April 6, 1916,. Serial No. 89,467. Renewed June 27, 1918. Serial No. 242,313.

To 0Z1, whom. it may concern:

Be it known that I, GUSTAF W. ELMEN, originally a subject of the King of Sweden, who arrived inlPhiladelphia from Sweden on August 1, 1893, when sixteen years of nection with cores for loading coils for telephone circuits. Its general object is to provide a new and improved core material which is cheap to manufacture, which is easily formed to the desired shapes, and which possesses to a high degree those characteristics most advantageous in cores for loading coils and other electrical apparatus.

The present invention may be considered an improvement upon the magnet core and process of manufacture described and claimed in an application for Letters Patent in the name of James Buckner Speed, Serial No. 89,409, filed April 6, 1916, for improvements in magnet cores, assigned to the same assignee as the present application. In the preferred embodiment of the Speed invention, as described in the application above mentioned, the core is composed of finely divided iron in the form of iron by hydrogen and insulating material, preferably a coating of red iron oxid, separating the particles of iron, said compound being compressed by pressure sufficient to give it aspecific gravity approximating that of the iron employed. While iron particles in the form of iron by hydrogen are soft and are therefore suitable for core making, the comparatively high cost of this form of iron, and the difficulties of obtaining it Without black iron oxid which is objectionable because it is magnetic and is notan insulating material, renders it unsatisfactory as a raw material for the manufacture of cores. It is, however, impossible to obtain satisfactorysoft iron particles by grinding up cast or other forms of soft iron, owing to the 'becomes a soft. mushy powder.

fact that such iron does not fracture into small firm particles of the size desired, but Nor is it possible to obtain satisfactory iron particles by grinding to the desired size hard iron such as the various forms of steel, because particles so obtained cannot be softened by annealing.

The present invention is the result of the discovery that iron obtained by electrolysis can readily be ground into particles of a size suitable for core making, and that said particles can be easily softened by annealing. The present invention, therefore, consists of a magnet core and method of mak ing the same, characterized by the fact that electrolytic iron is employed. and the further fact that the particles of such iron are annealed before they are compressed to form a core.

In the drawing, Figure 1 is a perspective view of a section of a loading coil core made in accordance with the present invention, and Fig. 2 shows a plurality of these sections assembled to form a complete core. It

merely illustrative, and that the invention is not limited to the production of this form of core, but isadapted for the making of cores of many forms, some of which cannot be made economically and satisfactorily of solid iron, plates or wires.

In the making of loading coil cores, the present invention is preferably carried out in the following manner: Electrolytic iron obtained in any well-known manner, (for example, from a cell containing a bath of ferrous ammonium sulfate), after being broken into small pieces is reduced to small particles by grinding in a ball mill. Experience has shown that for the best results, the particles used in core-making should not be larger in size than what will pass through what is known as eighty-mesh screen. Iron particles of this size are heated in any suitable form of furnace to anneal them and to drive off any occluded gases, principally hydrogen, and are then covered with a surface coating of insulating material, preferably red iron oxid. One method of oxidizing the particles which has been found satisfactory is to add to a mass of iron part1- .cles approximately 10% by weight of water, and then to heat and stir the mass in the presence of air until dry. The iron partiwill be understood, however, that this is Y cles 'Whichhave been obtained, annealed and covered with a surface coating of red iron 'oxid in the manner just described, are then ready for compression either into bulk materialffrom which cores may be made, or 'directlyinto the desired form of core.

The remainder of the'method of making magnet cores is substantially the same as that described in the Speed application for patent above referred to; but in order that this application may contain a full disclosure of the best method of carrying out the present invention, the remainingsteps of the method will be herein described.

The mold and press employed inthe. compressing process should be capable of standing and exerting exceedingly high pressures. I Preferably, pressures as high as two I hundred'thousand pounds to the square inch should be employed; and for the best results as to uniform density, the thicknessof any core section, in the direction in which the pressure is exerted in forming it, should normally not exceed approximately one-quarter of an inch. This consideration is so important that ithas been found desirable in making loading coil cores to use core sections even as thin as one-tenth of an inch, andto employ from twelve to fifteen sections in building up a core,-a suitable insula-ting material such aspaper, lacquer or shellac being interposed between the secv tions. tion or ring; and Fig. 2 shows thebuilt-up Fig. 1 shows such a core seccore. v

It has been found that cores made in the manner above described are strong mechanicallyand stable chemically; and that their specific gravity 1s approximately 7, which is nearly that of undivided iron, which is approximately 7, 7. Electrically,

' a loading coil core of this kind has high specific resistance, an extremely low hys- -teresis characteristic, excellent magnetic stability, and comparatively high permeability,

as understood in telephone loading coil design. The volume permeability of a core increases much more rapidly with increase of specific gravity, the more nearly the SPBOlfiQ'gIQVItY of the core approaches that In other words, increases of pressure are increasingly beneof undivided iron.

ficial as far as volume permeability is concerned, even though the intrinsic permeability of the particles has been lowered by reason of their compression. It has been found, however, that'the tendency of the oxid coating on the particles to puncture and thereby reduce the resistance of the core section, .makes it unwise to use pressures above a certain maximum "value. This value depends, of course, upon the char- 7 sure suflioient to and in experiments which led to t invention has been found to be pproxt per square inch s:

mately 200,000 pounds What is claimed is:

--acter of the oxid' coating on the particles,=1

h resent.

1. A magnet core composed joff' finely divided electrolytic iron, and insulating material separating the particles of the iron, said compound being compressed by pres-. sure suflicient to give it a specific gravity approximately the same as that of undivided iron.

1' 2. A magnet core composed of finely divided electrolytic iron, and insulating material separating the particles of the iron, said compound being compressed by presof approximately *3. A magnet core composed of finely divided annealed electrolytic iron, and insulating material separating the particles of the iron, said compound being compressed by pressure sufiicient to give it a specific-gravity approximately the same as that of undivided iron.

4c. The method of making magnet cores which consists in reducing electrolytic iron to a finely divided form, annealing theiron' give it a specific gravityv particles, coating said particles with ink sulating material, and submitting a mass said particles to pressure sufiicient to give the mass a specific gravity of approximately 7.

5. The method of making 'fnagnet cores which consists in reducing electrolytic iron to a finely divided form, annealing the iron particles, coating the surface ofsaid par-- ticles with red iron oxid, and submitting a mass of said'particles to pressure sufficient to form thevmass to the desired shapeand to give it a specific gravity of approxiically, grinding said iron into a finely divided state, annealing the iron particles, coating said particles with insulating iii? terial, and submittin "amass of said par-. ticles to pressure su cient to compress the mass into a self-sustaining solid.

In witness whereof, I hereunto subscribe my name this. 4th day of April, A. D., 1916.

eUs'rAF' w. ELMEN. 

